1. Field of the Invention
The present invention is generally related to a cooling system for a marine propulsion device and, more particularly, to a cooling system that intentionally induces nucleate boiling within cooling jackets of heat emitting components.
2. Description of the Related Art
Those skilled in the art of cooling systems are aware of the increased heat flux that occurs when a liquid changes state to a gas. During the process of nucleate boiling, a significant increase in the heat flux, from a heat emitting component, can be used advantageously in cooling systems.
U.S. Pat. No. 4,531,900, which issued to Jones et al. on Jul. 30, 1985, describes a rotary engine cooling system. A rotary engine has a substantially trochoidal-shaped housing cavity in which a rotor planetates. A cooling system for the engine directs coolant along a single series path consisting of series connected groups of passages. Coolant enters near the intake port, passes downwardly and axially through the cooler regions of the engine, then passes upwardly and axially through the hotter regions. By first flowing through the coolest regions, coolant pressure is reduced, thus reducing the saturation temperature of the coolant and thereby enhancing the nucleate boiling heat transfer mechanism which predominates in the high heat flux region of the engine during high power level operation.
U.S. Pat. No. 4,768,484, which issued to Scarselletta on Sep. 6, 1988, describes an actively pressurized engine cooling system. A coolant fluid is maintained in a state of nucleate boiling at a selected location in the coolant passages of an engine. The cooling system comprises a radiator and a coolant reservoir with a variable speed circulating pump for circulating the coolant through the coolant passages in the engine and through the radiator. A coolant pressure pump with a servo motor is adapted to pump coolant between the radiator and the reservoir as needed and to adjust the static pressure of the coolant.
U.S. Pat. No. 6,955,141, which issued to Santanam et al. on Oct. 18, 2005, describes an engine cooling system which has a diverter valve to selectively control the flow of coolant through an internal combustion engine having a cylinder block with a cooling jacket and a cylinder head mounted on the block with a cooling jacket. A controller, responsive to the temperature of the block and the head, controls the diverter valve and a water pump to provide adequate coolant flow through the head and the block as needed to maintain optimal operating temperatures. After the engine is shut off, the controller continues to operate the water pump and a cooling fan to continue to cool the engine for a period of time.
United States Statutory Invention Registration H2145, which was published on Feb. 7, 2006, describes mitigating ignition of fluids by hot surfaces. A platform, housing, conduit, exhaust duct or other structural element that encloses or supports a hot operating engine or other machinery is described wherein a pattern of micro-cavities is defined on the outer surface of the structure for mitigating ignition of a flammable liquid that comes into contact with the structure, the micro-cavities being sized to minimize seepage into the cavities of the liquid because of its surface tension, thereby preventing wetting of the interior of the cavities by the liquid.
U.S. Pat. No. 7,028,763, which issued to Garner et al. on Apr. 18, 2006, describes a cooling arrangement and method with selective surfaces configured to inhibit changes in boiling state. Heat transfer in coolant circuits, as in an internal combustion engine, for example, can be beneficially enhanced by maintaining the coolant in a nucleate boiling state, but undesirable transitions to a film boiling state are then possible. The coolant circuit has selected surfaces that have a tendency to experience high heat flux in comparison to adjacent surfaces in the cooling circuit. These surfaces are provided with a surface configuration, such as a matrix of nucleation cavities, which has a tendency to inhibit a change in the boiling state.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
It would be significantly beneficial if a marine propulsion system could be provided with a means for causing nucleate boiling to occur within the cooling jacket of an engine or within other heat emitting components of the marine propulsion system. More specifically, it would be beneficial if the cooling system that combines both closed loop and open loop portions could be provided with the benefits of nucleate boiling within the closed loop portion.